This invention relates to a back-driving silent chain, and in particular, it relates to a guide link for a back-driving silent chain that has window portions to reduce the stiffness or rigidity of the link. The chain has a plurality of rows of links that are interleaved and connected by a connecting pin inserted in the apertures of each of the link plates. In its preferred embodiment each row comprises multiple link plates, each with a pair of apertures and a pair of teeth on both sides of the aperture or pinhole center line. The link plates have guide links positioned on the outermost side of the link plates. The invention relates to an improvement in the construction of the guide links.
Silent chains are used conventionally as power transmission chains for automobiles and motorcycles in transmissions and transfer cases for four-wheel drive vehicles. In general, a silent chain is comprised of multiple link plates, each of which has a pair of teeth. Each link typically includes a pair of apertures. The links are interleaved and are connected by connecting pins placed in the apertures. Guide links are positioned on the outermost side of the link plates and the ends of the connecting pins are press fit into apertures in the guide links.
FIGS. 7 and 8 show examples of a conventional low-rigidity or low stiffness guide links. FIG. 7 shows the guide link disclosed in Japanese Utility Model No. 4-52641 ('641) (U.S. Pat. No. 5,176,586). In this case, guide link 100 has pinholes 101, 102 and window hole 103. As is clear from the shape of pinholes 101, 102 and lines 1-2 of the '641 specification, the silent chain with guide link 100 is the rocker joint-type silent chain that uses a rocker joint composed of a pair of long and short connecting pins and pinholes 101, 102 that secure the press-fit end of the longer pin of the rocker joint. Incidentally, single-dot line 110 in the figure indicates the pinhole center line.
When the silent chain comprising multiple link plates and guide links such as guide link 100 is operated, tension acts along the entire length of the chain. Tensile force applied through the connecting pins, in the direction to expand the aperture center distance (or pitch), acts on the apertures 101, 102 of the guide links and on the apertures of the link plates. Because the rigidities or stiffness of the inner links differs from the stiffness of the guide links, the connecting pins of a conventional silent chain can be deformed or possibly fractured.
Therefore, various ideas have been implemented in the past to equalize the elongation of the guide links and inner links caused by the tensile load (tensile rigidity). The tensile load is applied during chain operation or, more commonly, during a preloading or pre-stressing operation after assembly of the chain.
FIG. 8 shows the guide link disclosed in Japanese Laid-Open Patent Heisei 4-210144 ('144) (U.S. Pat. No. 5,345,753) and guide link 200 has pinholes 201, 202 and slit 203. As is clear from the shape of pinholes 201, 202, the silent chain with this guide link 100, too, is a rocker-joint-type silent chain and the end of the longer pin of the rocker joint is press-fit in apertures 201,202. Incidentally, single-dot line 210 in the figure indicates the pinhole center line.
For these guide links, the tensile rigidity of the guide link is lowered by formation of a window hole 103, 203 or slit. That is, the guide link is made to deform or elongate equally with the link plate against the tensile load, to prevent deformation of the rocker joint.
However, the conventional guide links are guide links for the rocker joint, as shown in FIGS. 7 and 8. Material thickness d at the edge of pinholes 101, 102 and window hole 103 differs from material thickness d' at the pinholes 201, 202 and slit 203. Depending on the position of the pinhole, the press-fit between the end of the pin of the rocker joint and pinhole may not be secure.
In the example in FIG. 8, although the material thickness d' at the edges of slit 203, pinholes 201, 202 looks sufficient in the figure, the material thickness can be considerably less locally at the edges of the pinhole and slit as shown in FIG. 7. If the round pinhole of the guide link 200 is changed to receive a round pin, while a similar slit, 203, is utilized, decrease of the force that secures the end of the rocker joint pin in the pinhole can occur easily.
On the other hand, in the case of the back-driving silent chain, which includes links with pairs of teeth on both sides of the centerline between the apertures, the thickness of the guide link must be sufficient to ensure the contact area between the chain and the shoe of an associated chain tensioner arm. Thus, the rigidity of the guide link is higher than that of the normal guide link. Therefore, a low-rigidity guide is strongly needed, especially for the back-driving silent chain.
This invention addresses the above-described situations and its purpose is to offer a back-driving silent chain of low rigidity that does not result in the decrease of the fitting force between the pinhole of the guide link and the connecting pin.